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Rational number word problem: stock

Use your knowledge of proportions and fractions to determine shareholders profit in this word problem. Created by Sal Khan.

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• how come sal divided 4,200 by 4,200 and 4,050 and 2,510?
• Sal did that because you have to divide Mary's shares by the total amount of shares. If you have 4 slices of pizza, you ate 1 of the 1+1+1+1 pieces. If you did not include the slice of pizza you ate (Mary's shares), you would've gotten 1/3. That is why you need to include Mary's shares in the denominator along with the other two.
• Why did Sal divide 4200/(4050+250+4200) to get the answer?
I just don't get it because dividing Mary's shears by everyone get the answer.
• Haha ... Mary's shears? Didn't know she was a gardener now. :D
Ok, now to answer your question. Sal wanted to simplify the fraction and the only way to do that was to divide. As you know a fraction is basically a stood-up division problem so that's why he divided. Once he simplified it, it was a decimal . The decimal is how much of the shares she owns.
• woah woah woah... why is our math teacher using a calculator?
• because it would take FOREVER to do it without (trust me, I know) and in order to be able to do this kind of math on a calculator, you still have to know the equations. In short, it saves brainpower.
• why's he using a calculator, he should get a piece of paper or something and do it himself
• he pretty much just did it in front of us. Sal uses the drawing app he uses to show us how to solve the problem, and then he sometimes uses a calculator to check his own work to make sure HE didn't make a mistake and wouldnt have to re-record the video. we are all human, so it is very important to check our work for possible mistakes, but it is also important to know how to solve things on paper. :)
• why does the calculator look so real?
• It's just the program he uses. Kinda pointless if you ask me
• another way of doing it is adding the amounts of shares up and dividing by 1.5 million then just multiplying the answer by 4200.
• Nope. Each shareholder has DIFFERENT amounts of shares, so they don't make the same amount of money.
• if you guys are confused, here's another way to think about it

By finding the sum of all shares, which is 10760

and then lets divide \$1,500,000 with 10760,

which will get us : \$139.4 = per share

since mary has 4200 shares, we just multiply it amount of money per share :

139.4 x 4200 shares = \$585,501.85....